For recently manufactured electric appliances (such as, an FPD (Flat panel display) and a thin-film solar cell), transistors need to be uniformly arranged on a wide substrate; and thus, (hydrogenated) amorphous silicon or the like is used, in which a semiconductor layer having uniform properties can be formed on a large-area substrate.
The amorphous silicon can be formed at low temperature and thus, does not adversely affect other materials. However, the amorphous silicon has a disadvantage of low mobility; and thus, oxide semiconductors, in which a thin film with high mobility can be formed at low temperature on a large-area substrate, attract attention.
On the other hand, in recent years, a low-resistance copper thin film has been used as electrodes and wiring for transistors in a semiconductor integrated circuit or a FPD so as to increase the transmission speed of a digital signal and achieve a reduction in the power consumption due to a reduction in power loss.
However, if the wiring layer in a semiconductor integrated circuit is formed from a copper thin film, there arise disadvantages in that the copper thin film has poor adhesion to an oxide and that the copper atom, which is a constitutive substance of the copper thin film, also easily diffuses into the semiconductor or the oxide.
Accordingly, major problems of the copper wiring on an oxide thin film are peeling and copper diffusion.
As a countermeasure to such problems, a barrier film for improving the barrier properties against diffusion and increasing the adherence strength of the copper thin film can be provided between the copper thin film and the oxide thin film contacting the copper thin film. The examples of the barrier film include a TiN film, a W film or the like.
However, the copper thin film is difficult to be dry-etched; and thus, wet etching is usually used. However, since an etchant for the copper thin film differs from an etchant for the barrier film, a wiring layer with a two-layer structure of the barrier film and the copper thin film needs to be separately etched by changing the etchants, with the use of barrier film in a conventional art.
Therefore, there is a need for a wiring layer which has the barrier properties and the adhesion properties and which can be patterned by one-time etching.